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spec: fix forwarding-references-upwards header org, add downwards blurb.
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dtzSiFive committed Mar 6, 2023
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Expand Up @@ -1919,7 +1919,7 @@ module RefProducer :
define thereg = probe(myreg)
```

### Forwarding References Upwards
#### Forwarding References Upwards

Define statements can be used to forward a child module's reference further up
the hierarchy:
Expand Down Expand Up @@ -1951,6 +1951,26 @@ module Forward :
define p = f.p[0][1]
```

#### Forwarding References Downwards

Define statements can also be used to forward references down the hierarchy
using input reference-type ports, which are allowed but should be used
carefully as they make it possible to express
invalid reference paths.

See [@sec:input-references] for more details, a small example is given below:

```firrtl
module UnusedInputRef :
input r : Probe<UInt<1>>
module ForwardDownwards :
input in : UInt<1>
inst u of UnusedInputRef
define u.r = probe(in)
```

### Force and Release

To override existing drivers for a `RWProbe`{.firrtl}, the `force`{.firrtl}
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